Hand-held electrical probes are known in the art for detecting the presence of AC signal potential on a conductor. The probes are either of a contacting type which requires direct electrical contact with an uninsulated portion of the conductor, or of a noncontacting type which senses the resulting electromagnetic field when placed in proximity to the conductor. There is a safety risk associated with the contacting type probe due to the possibility that the user may receive a harmful electrical shock, so that the noncontacting type probe is preferable.
Since both type probes use a visual and/or audible indicator to annunciate the presence of a detected voltage potential to a user, many of the probes have manual on/off switches that allow a user to deactivate the probe when not in use. The switch, however, presents a number of disadvantages. If the switch is made of metal, it can act as a conduit to shock and injure the user if the switch comes in contact with a “live” wire or circuit. A user may forget to turn the switch on before using it, thereby risking a false negative reading, or a user may forget to turn it off causing the batteries to run down. A manual on/off switch can also break with repeated usage over an extended period of time. Therefore, it is preferable for a user to have a probe that does not rely on the use of a manual on/off switch.
U.S. Pat. No. 5,103,165 discloses an improved, switchless type probe that may be contacting or noncontacting. In a best mode embodiment the '165 probe housing comprises non-conductive material, such as polyvinylchloride (“PVC”), to reduce the risk of electrical shock for a user, and it eliminates the use of a switch through the use of internal circuitry that automatically activates the probe when it senses an electrical current or voltage, thereby reducing the drain on the batteries. The probe disclosed in the '165 patent provides a visual indicator to alert the user to the presence of an electrical current or voltage, but does not have an audible indicator. The insulated housing of the '165 probe, however, presents a problem with static charge build-up, which causes flickering of the visual indicator and would cause chirping of an audible indicator. The static build-up may occur when the probe is rubbed on cloth, such as a user's pocket or sleeve. This intermittent flickering and/or chirping may be annoying to the user, and it would also drain the batteries.